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Battery information/calculation?

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Old 12-15-2006, 12:28 PM
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hawk3ye
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Default Battery information/calculation?


hi all,

I was just trying to figure out if my Lipo would work properly with a certain set of brushless motors - is there a calculation somewhere where I can figure this out?

Thanks!

Setup in question:

-11.1v 2100mah Lipo
-EMI BLS 2629-10-100 1000KV B/L Motor (TWO of these)
-18A Brushed Speed controller
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Old 12-16-2006, 09:02 AM
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Default RE: Battery information/calculation?

Are you trying to figure out how long you will be able to fly? Or just if the motors will operate? If the LiPo has a C rating that is high enough to handle the amp draw of the two motors running simultaneously, and the motors are rated to handle the 11.1 volts the battery has to deliver, and your ESC's are rated to handle the amp draw of both motors running at the same time and has a LiPo auto cutoff function.......etc..... you should be fine. A little more specifics would help. The C rating of the battery, are you indeed trying to run both motors at the same time off of the one ESC, what brand is the ESC, what is the amp draw range, continuous current and max. burst of the motor?
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Old 12-16-2006, 10:30 PM
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packyj
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Default RE: Battery information/calculation?

Not sure you can run two brushless motors with one esc... surely not off of one 18A brushed esc unless that was a typo... but with motor timing and such two esc's is the only way i know to run a dual motor setup with brushless
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Old 12-18-2006, 10:17 AM
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Default RE: Battery information/calculation?

hhmm, weird, my last post didn't go up - I'm sorry if I seemed rude and didn't respond in a timely manner.

Thank you both for the responses...here's the ESC info and my Lipo battery info.

Battery:
2100mAh 3-Cell 11.1V LIPO,16GA
Maximum Continuous Discharge : 15C
Maximum Burst Discharge : 20C
Maximum Continuous Current : 31.5A

ESC, this is the one foudn on the kit linky - there's a list of recommend parts I guess:

ESC:
Gold Heart (LITON) 12A Brushless ESC

Maximum load (in 10 seconds) 15A, for constant use: 10A
Working voltage: Ni-CD / Ni-MH ----- 6 to 12 cell (6-15V)
Li-ion / Li-polymer ----- 2 to 4 cell (6-15V)
Working temperature: 0 ¢J - 50 ¢J
Maximum RPM: 2-pole motor / 210,000 rpm
6-pole motor / 70,000 rpm
12-pole motor / 35,000 rpm

http://www.infinity-hobby.com/main/p...roducts_id=597

Brushless motor:

EMI BLS 2629-10-100 1000KV B/L Motor x 2

http://www.infinity-hobby.com/main/p...e80c5fdfd596dd


Main Airplane Product Linky:
http://www.infinity-hobby.com/main/p...roducts_id=602
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Old 12-18-2006, 10:47 AM
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Default RE: Battery information/calculation?

Wooooops........forgot to include the fact that packyj brought up. You DEFINITELY need one ESC for each motor. I was more talking about one battery handling both motors. I believe you can Y-harness one battery to run both, but your flight times will be very low, and with the specs. provided, you would be pushing that battery to the limits running both motors off of it. The prime setup is one ESC and one battery per motor. You could get a larger capacity single battery and Y harness it. All a matter of opinion and preference.

The link to the motor really does not say what the motor is going to pull as far as amps on a continuous and max. burst rate? But they do package the ESC with it as a combo, so you would hope it would work But at a max. of 15amps, X2 for both motors = 30amps, you are right at the max. cont. for the battery, and it will most likely get stressed and not have as long of a life under those conditions.

The setup in general looks ok, it is just a matter of deciding on one battery per ESC, or one larger battery Y harnessed to both ESC's. I would definitely recommend getting a power meter or watt meter of some kind and measuring the draw of the system with your prop selection and both motors running to make sure you know what your amp pull from the battery is at.
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Old 12-18-2006, 11:33 PM
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Default RE: Battery information/calculation?

hiya FLip!

guess what, I found another thread which is more detailed on this bird (linky below). I Was reading it in it's entirety (all 30+ pages) and I found the AMP draw...

So my Lipo is...a 2100mah 11.1 volt...how much air time do you think I can get with the info below?

Brushless motor, EMI BLS 2629-10-100 -- 1,025KV

Powered with 3cell Li-Po and EMI 8.5x8 Prop. draw 12Amp each at full throttle, get 6,300 rpm. Prop Pitch speed 75.6 Km/Hr (46.4 MPH).

At cruise speed, twin motors draw totally around 10.0~12.0A, get 4,000~4,500 rpm. Prop Pitch speed 48~54 Km/Hr.(29.4~33.75 MPH)

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Old 12-19-2006, 12:12 AM
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Default RE: Battery information/calculation?

According to your listed amp draw of 12 amps per motor x 2 = 24 amps total draw at FULL throttle, the runtime running off one 2100 lipo will be about 5 minutes and 15 seconds, and if cruising at ~11 amps, make that about 11 minutes. Now that's with a theoritical *average* amp draw of 24 amps. Your numbers may vary in real life; wind, or no wind, weight of the airplane, your own flying habits, and such.

Since that battery is rated for about 30 amps constant, you should be alright, but again, that's assuming that the *maximum* amp draw at *full* throttle is 12 amps per motor. I'd still try ot use a higher C rating, or higher capacity battery just to be safe. Plus having a higer mah battery means more runtime. I think Thunder Power makes a 3000 mah or similar 3-cell battery that should work well in this case. That should give you ~8 minutes of flight at full throttle, and about 16 minutes cruising.

Make sure your ESC and battery(ies) gets enough cooling airflow to be safe.
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Old 12-19-2006, 10:08 AM
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Default RE: Battery information/calculation?

Heya thanks for the reply as well Slo-V (I love my slo-v planbe btw) - I'll have to do some reading on that battery, I found one on the HobbyTown website but it didn't mention the dimensions.

quick newbie question though - I have a PZ Focke Wulf that I use my 3 cell 2100 mah Lipo in...would I be able to use a 3200mah 3 cell in it as well without doing any damage? I'm hunting around for a battery info link but I thought I'd ask realyl quick. Thx!
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Old 12-19-2006, 10:51 AM
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Default RE: Battery information/calculation?

Ya, as slo-v stated, with the first option, 12 amps per motor = 24 total = 5.25 minutes.

You could theoretically use that 3200mah pack, it is still 3S, so the 11.1 volts stays the same which is the important number. The mah number is just the capacity, runtime basically. However, going from a 2100mah to a 3200mah is a big jump in weight. It will throw off your COG in the plane and the plane will fly heavier and slower.
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Old 12-19-2006, 11:05 AM
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Default RE: Battery information/calculation?

I see.

I'm wondering if I should use the kit's stock motor setup instead then. I noticed in this (huge) [link=http://www.rcgroups.com/forums/showthread.php?t=577451&page=35&pp=15]thread [/link] about the plane that a lot of guys were able to use a 2 or 3 cell 2100m ah Lipo pack just fine with the stock dual 370 brushed motors....

I guess my next question would be to ask about the ESC and Y harness since i'd like to use a single battery. I noticed in the PZ Focke Wulf that there's no ESC pieces, it looks like everything hooks up into a little circuit board with everything in it - when I look to buy ESCs, I should make sure they are Lipo compatible correct? or is it the receiver that I need to make sure is Lipo compatible?

Also, for the Y harness, could someone please post for me a link where I can read up on an example?

THanks again fellas!
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Old 12-19-2006, 03:05 PM
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Default RE: Battery information/calculation?

Yes, the ESC needs to be LiPo compatible.

I think this is what you are looking for in a 'Y' harness http://www.e-fliterc.com/Products/De...odID=EFLAEC307
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Old 12-19-2006, 05:49 PM
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Default RE: Battery information/calculation?

hiya, thanks again. That looks simple enough!

Btw, a response about flight times from a guy using the brushless motors I outlined above with the plane was somewhere around 8 minutes. I looked into bigger MAH battery but i think the size would cause issues - the battery cockpit gets awfulyl small with all the electronics and I guess I have to account for heat as well
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Old 12-19-2006, 06:41 PM
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Default RE: Battery information/calculation?

Ya, you don't want the ESC, motor and battery all sharing a small space.....that is a recipe for an airshow smoke spectacular [:-]

The link I posted was for attaching 2 LiPo's to a single ESC......It sounds like you are looking for a "y" harness to connect a single battery to 2 ESC's correct? It will be similar to that, but not exactly the same.
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Old 12-20-2006, 09:57 AM
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Default RE: Battery information/calculation?

Yep a Y harness for a single battery and two motors

Yeah the motors are parked off to each side and the main cockpit is where the ESC/receiver/battery will go.
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Old 12-29-2006, 12:37 PM
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Default RE: Battery information/calculation?

Heyas,

I have another quick question...

I was reading some more responses to people's engine setups for the plane i'm interested in building (twin brushless motor p-38) and i noticed the guys were saying that the current draw was like 18 amps...if I'm buying two ESCs (one for each motor) that are 18 amp each that would be a combined 36 amp - couldn't I get away with two 10 AMP ESCs then? or am I misunderstanding the concept... I'm curious if I was understanding the application in the above question.

I read that using a high AMP ESC is a good thing to reduce hear etc - what are other advantages?

Ty in advance.
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Old 12-29-2006, 12:59 PM
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Default RE: Battery information/calculation?

You have to look at it as an individual setup for each motor. Each motor has it's own independent ESC. So if the current draw of one motor is 18 amps, then that motors' ESC needs to be able to handle the 18 amps independently. Each side is it's own, completely seperate setup.

Now, if it is a combined draw of 18 amps, so 9 amps per each motor individually, then yes, you could get a 10 amp ESC for each side. It is always better to have some room rather than just barely squeaking by. The main advantage is less stress on the system by going over on the ESC amp rating. It stays cool and will last a long time.
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Old 01-02-2007, 11:52 PM
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Default RE: Battery information/calculation?

heya sorry to bump such an old topic but i thought the history would help give background to the question....

So (summary) my P-38 will have to brushless motors with an ESC to each one and a Y harness powering the ESCs which in turn govern the juice to the motors...

I looked at a guy's pic of this setup [link=http://www.rcgroups.com/forums/attachment.php?attachmentid=1105083]Infinity P-38[/link] you can see that he's got the Y harness I was trying to reokicate - but I think i'm a little confused as to how the receiver gets it's power...a buddy of mine tried to explain this to me and it sounds like the "power" wires from the ESCs need to come together in another Y harness to connect to the plane's receiver, am I wrong?

thanks!
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Old 01-03-2007, 11:13 AM
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Default RE: Battery information/calculation?


ORIGINAL: hawk3ye

I looked at a guy's pic of this setup [link=http://www.rcgroups.com/forums/attachment.php?attachmentid=1105083]Infinity P-38[/link] you can see that he's got the Y harness I was trying to reokicate - but I think i'm a little confused as to how the receiver gets it's power...a buddy of mine tried to explain this to me and it sounds like the "power" wires from the ESCs need to come together in another Y harness to connect to the plane's receiver, am I wrong?

thanks!
No, I think you are correct. You will need a 'Y" harness that you would use to connect two servos to the same channel, to connect the two ESC's to the same channel.
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Old 01-04-2007, 09:18 AM
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Default RE: Battery information/calculation?

Thanks again FLipProb17!

Wooo...now I'm all straightened out on this...I was reading some more on the topic of the EMI P-38 and there was mention of "mixing" where if the rudder was to say turn left or right - the engines would increase/decrease to one particular side as well - would this be hard to set up? I was thinking about this and i dont quite see how this could work, maybe I misunderstood the posting....

help?
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Old 01-04-2007, 10:21 AM
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Default RE: Battery information/calculation?

Honestly, I would not deal with mixing until you get somewhat use to the plane. Especially mixing the rudder with the throttle, just seems a little funky to me. And even when you get use to it, I might not even deal with it. I do not have a multi-fngine plane, so maybe mixing the rudder and throttle makes sense there (somehow), but on the planes I do fly I have not mixed any channels on any of them yet. If you are not 100% sure/exact about what you are mixing and the rates that you apply to each channel, you can get in trouble inn a big hurry. It still just seems weird to mix the throttle with the rudder. Ya, one side powers down while the other side stays running, it just helps you turn/manuever, it really just sounds like an experienced way to get more performance and quicker handling out of the plane. I would just go with the good ole' regular setup, at least until you get use to her.
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Old 01-05-2007, 10:56 AM
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Default RE: Battery information/calculation?

Ah ya know...I just spent some time finding the actual post...the guy didn't actually use the rudder, but he made motors mix so that they'd act as a ruder, check out this setp-by-step.

It looks a bit over my head atm but I'd love to try it when I get a better understanding of the electronics one day.

Btw, I'll have a 6 channel Futaba 6exa and matching 6 channel receiver.

---------------------------------------------------------------
My Tx is a Futaba 7CH (same procedure applies to the 7CA, and probably the 9C's as well). For other brands, the procedure should be similar...

1. Use the normal channel 1 (and a Y-connector) for ailerons, or turn on the flaperon function and use channels 1 and 6 for right/left aileron plus flap capability. The following throttle setup has no effect on this part.

2. Nosewheel servo goes to channel 4, as always.. again, unaffected by the following throttle setup.

3. Use a programmable mix to slave channel 5 to channel 3, 100% mixing. This in effect creates two separate throttle channels (3 and 5) for the two ESCs.

4. Use a second programmable mix with channel 4 as master and channel 3 as slave, using +50% mix to start.

5. Use a third programmable mix with channel 4 as master and channel 5 as slave, with -50% mixing to start.

In this manner, channels 3 and 5 (ESCs) follow the throttle stick in unison, and when the rudder stick is moved, you effectively 'add' throttle on one side and 'subtract' throttle on the other. NOTE the following considerations:

An ESC cannot be 'overdriven' like a servo, so there's no problem if the combined throttle signal goes above 100% or below 0%. The ESCs simply ignore the 'excess'.

It's important to use ESCs that have a "Fixed Throttle Range" parameter so that the two ESCs retain their settings for channels 3 and 5. This is why Castle doesn't recommend using Thunderbird ESCs for multi-engine, although it seems to me that any variance could be corrected with rudder trim, which in this setup really becomes 'engine RPM synchronization' in addition to nosewheel centering.

The initial setting of 50% mix is just a starting point, and will probably have to be adjusted for the in-flight effectiveness. My initial tests 'on the floor' showed that 50% provides enough throttle differential to yaw the plane sideways in your hands. This will likely NOT be the case at flying speed when the fixed rudders take effect.

You may have to swap the ESC plugs in channels 3 and 5 (or swap the plus and minus mix settings) so that the proper motor accelerates when moving the rudder stick. LEFT rudder should cause the RIGHT motor to increase RPM.
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Old 01-05-2007, 12:41 PM
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Default RE: Battery information/calculation?

hawk3ye, I'm with fliprob on the rudder /throttle mixing, that's a lot to get into, for, from your questions sounds like a beginner. If need be PM me I can take some photos of mine for you so you can see how it's set up with the Y harness's and such. Mines the bright red "YIPPEE" one in the forums.

A twin is double the trouble and twice the fun.

Also something else, before buying the brushless setups from EMI, you should check out some other sources. The motor/esc combos in mine were $45.80 for 2 brushless motors and esc's.

Oh and lastly, there is no such thing as a dumb question. Dumb is doing something and then having to ask why it didn't work.
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Old 01-05-2007, 07:00 PM
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Default RE: Battery information/calculation?


Heya Thx Glacier Girl, no worries, I get all excited about learning new stuff that I tend to overload myself with crazy ideas and stuff all the time heh

Thanks for the hint about the brushless setup too, i think buying outside of Inifinity would save a good chunk of money for sure...I'll let the GF know...she's getting me the setup for my birthday Wo0t!
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Old 02-05-2007, 02:35 PM
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Default RE: Battery information/calculation?

What do the instructions from the motor manufacturer say about the operating current of the motors?

Joshua Gordon
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